1. Field of the Invention
This invention pertains to a method for partially annealing the sidewall of a container, and more particularly to a method of thermally treating portions of a sidewall of a drawn or drawn and ironed container body to render the container sidewall capable of being bulged successfully.
2. Description of the Art
Various methods are known in the art for shaping articles, such as drawn metallic containers. U.S. Pat. No. 1,711,445, for example, discloses a method in which a plunger and compressed air cooperate to bulge container sidewalls against the face of an adjacent die. U.S. Pat. No. 2,787,973 pertains to a method for hydraulically expanding a container into tight contact with a surrounding mold. High voltage discharge forming of containers against a fixed mold is described, for example, in U.S. Pat. No. 3,654,788. Also, electromagnetic forming, disclosed in U.S. Pat. Nos. 3,383,890 and 3,599,461, involves the generation of a pulse of electromagnetic force against the sidewalls of an adjacent container to reform the container.
Additionally, the prior art teaches the use of induction heating for the purpose of annealing tubular articles prior to subsequent forming operations. For example, U.S. Pat. No. 3,413,432 discloses the induction heating of a metal tube prior to circumferentially enlarging the tube ends. U.S. Pat. No. 4,307,276 pertains to a method of uniformly heating long steel pipes by passing the pipes through one or more induction heating coils to heat treat the pipe.
Despite the prior art teachings in the area of container shaping, and in the area of annealing, there is no teaching of preferred methods of thermally treating selective areas of a container sidewall prior to shaping. In particular, there is a need for a method for partially annealing selective areas of the sidewall of a container to selectively reduce the yield strength and increase formability in such areas to permit successful subsequent bulging of such thermally treated areas.